BPOZ is one protein containing ankyrin repeat and BTB (POZ) domain which gene is located at 3q21.3 in human genome. It was found that the expression of BPOZ gene is down-regulated in human ovary tumors, suggesting it is potentially a cell growth or tumor suppressor gene. BPOZ gene knockout mouse model was established for further in vivo study of its normal function and the role of BPOZ in tumorigenesis. The mouse genomic DNA sequence of BPOZ gene was verified through bioinformatic analysis. According to the BPOZ genomic DNA sequence, the strategy of gene targeting and constructing of knockout vector (XpPNT-BPOZ) were established to delete the region of mouse genome, which spans from exon 2 to 12 of BPOZ gene. The gene knockout vector XpPNT-BPOZ was constructed and confirmed by restriction enzyme digestion and sequencing. Electroporation of ES cells with XpPNT-BPOZ and screening of both G418 and Ganciclovoir resistant clones were performed according to common protocol. The homologous recombined ES cell clones were identified by PCR and confirmed by Southern blot analysis. After transplantation of homologous recombined ES cells into blastocysts through microinjection and mating of chimeras with C57BL/6J mice, 30 offspring with Aguoti fur in color were acquired. 15 of them (50%) show genotype heterozygous for BPOZ. The BPOZ heterozygotes were intercrossed to generate mutants homozygous. Finally, the cohort of mutants homozygous for BPOZ was established. The mutants are fertile, and further phenotype analysis is under way.